CIRRATULID^E. 237 



between the divisions of the feet. It agreed with the other examples in having six bristled 

 feet in front of those with the long club-shaped processes. 



Claparede made comparisons of this unknown larva with Polydora and Magelona, but 

 he did not definitely connect it with the Spionidae. 



The pelagic young of this form had long been known in the tow-nets at St. 

 Andrews, yet up to date no adult example has ever been procured. An account of the 

 various stages was given in 1894, 1 the youngest having about twelve bristled segments, 

 and the most advanced about fifty segments. The long provisional bristles, the feet, and 

 the lateral pigment-spots are characteristic. More advanced forms are represented in 

 Plate XCIV, figs. 15 and 15 a, both having so many of the adult characters that their 

 relationship is readily made out ; the latter being procured in July, the former in October. 



Bisoma. — So far as known, this form, which occurs in the Cattegat and other 

 regions, has not yet been procured in British seas, but its pelagic larva should be looked 

 for in the tow-nets in the North Sea. 



Family XXII. — Cirratulim], Holmgren. 



Head distinct but small, always devoid of appendages. Buccal segment with 

 ventral mouth; proboscis always unarmed. Two achaetous segments follow. Body linear, 

 filiform, elongated, with numerous narrow rings. Tentacles present or absent, dorsal or 

 ventral (prehensile?). Branchise long, filiform, contractile, dorso-lateral in position, in 

 many or a considerable number of segments. The corpuscles in the blood of G. chryso- 

 derma, Claparede, are flattened-fusiform in shape. In this and others their colour is 

 identical with the liquid in which they float. Feet biramous, divisions separate ; without 

 setigerous processes or appendages ; superior division generally with capillary bristles, or 

 with bristles and crotchets ; inferior division with shorter bristles or with these and 

 crotchets or crotchets alone. 



In Girratulus tentaculatus the body-wall has externally a thin cuticle over the 

 hypoderm with areolse and glandular cells internally. Beneath is the thick basement- 

 membrane, internally a thin circular muscular layer which is continued external to the 

 nerve-area across the mid-ventral line, the neurilemma and neuroglia intervening between 

 it and the cords proper, around which, and especially ventrally and laterally, numerous 

 deeply-stained cells of the neuroglia occur, the middle region below the nerves being 

 often opaque from this cause, and on cross-section reticulations spread upward to the 

 cords. Moreover the region between the cords and the basement-tissue of the hypoderm 

 varies in extent, apparently from the stretching cf the tissues. At the ganglionic 

 enlargements the vertical area is considerably increased, and in some sections two small 

 neural canals are present under the cords on each side of the middle line. The two cords 

 are distinct in the interganglionic areas, surrounded by their investments. A median 

 mesentery fixes the ventral blood-vessel over them, and the slender oblique muscle is 

 attached to the upper and outer angle of the area. The dorsal arch is formed of the 

 cuticle and hypoderm, then follows a dense layer of basement-tissue which does not 

 1 ' Quart. Journ. Micr. Sc./ vol. xxxvi, N.S., p. 71, pi. viii, figs. 4 — 7. 



